High-definition television

Projection screen in a home theater, displaying a high-definition television image.

High-definition television (HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (standard-definition TV, or SDTV). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.

History of high-definition television

Further information: Analog high-definition television system

The term high definition once described a series of television systems from the 1930s and 1940s, starting with the British 240 line and 405 line black-and-white systems introduced in 1936, and including the American 525-line NTSC system established in 1941. However, these systems were only "high definition" when compared to earlier systems.

The British high definition TV service started trials in August 1936 and a regular service in November 1936, using both the Baird 240 line and Marconi-EMI 405 line systems. The Baird system was discontinued in February 1937.

A brief itemized history of early analog HD systems follows; these would be considered standard definition television systems today.

1936: System-A, UK: 405 lines @ 50 Hz, discontinued 1986

1938: Several countries used a 441 line system, France in 1956 being the last to discontinue it

All used interlacing and a 4:3 aspect ratio except the 405 line system which started as 5:4 and later changed to 4:3.

The post–World War II French 819-line black-and-white system was high definition in the contemporary sense, but was discontinued in 1986, a year after the final British 405-line broadcast. Experimental 405 line color transmissions were made in the 1950s using a modified NTSC system.

Since the formal adoption of DVB's widescreen HDTV transmission modes in the early 2000s the 525-line NTSC (and PAL-M) systems as well as the European 625-line PAL and SECAM systems are now regarded as standard definition television systems. In Australia, the 625-line digital progressive system (with 576 active lines) is officially recognized as high definition.[1]

Color

In Mexico, Guillermo González Camarena (1917–1965), invented an early color television transmission system. He received patents for color television systems in 1942 (U.S. Patent 2,296,019), 1960, and 1962. The 1942 patent (filed in Mexico on August 19, 1940) was for a synchronized color filter wheel adapter for monochrome television, similar to the field sequential color receiver demonstrated by Baird in England in July 1939[53] and by CBS in the United States in August 1940. _|_

On August 31, 1946, González Camarena sent his first color transmission from his lab in the offices of The Mexican League of Radio Experiments at Lucerna St. #1, in Mexico City. The video signal was transmitted at a frequency of 115 MHz and the audio in the 40 meter band. He made the first publicly announced color broadcast in Mexico, on February 8, 1963, of the program Paraíso Infantil on Mexico City's XHGC-TV.

In 1958, the U.S.S.R. created Тransformator (Russian: Трансформатор, "Transformer"), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of television conferences among military commands; as it was a military product, it was not commercialized.[2]

Modern systems

In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard.[3] However, the system was not launched publicly until late in the 1990s.

In 1981, the first HDTV demonstration in the United States was held. It had the same 5:3 aspect ratio as the Japanese system.[4] Upon visiting a demonstration of the Japanese Multiple sub-nyquist sampling Encoding system (MUSE) HDTV system in Washington, U.S. President Ronald Reagan was most impressed and officially declared it "a matter of national interest" to introduce HDTV to the U.S. Several systems were proposed as the new standard for the U.S., including the Japanese MUSE system, but all were rejected by the FCC because of their higher bandwidth requirement.

A new standard had to be radically efficient, needing less bandwidth for HDTV than the existing NTSC standard for SDTV. It was commonly understood only a digital system could possibly bring desired results, however nothing such had yet been developed. Pattern-recognition research for cruise missile development at the NASA Jet Propulsion Laboratory provided the basis for developing the MPEG set of compression standards.

The rise of digital compression

As soon as the MPEG-1 standard provided the foundation for digital TV, development of modern TV standards started worldwide. After finalization of MPEG-2 in mid 1993, the DVB organization within the International Telecommunication Union's radio telecommunications sector (ITU-R) developed the ETSI standard 300-327 by the end of December 1993.

It became known as DVB-T for digital terrestrial TV. DVB-S and DVB-C standards soon followed for terrestrial, satellite, and cable transmission of SDTV and HDTV. In the U.S. the Grand Alliance proposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on the MPEG-2 standard. The DVB-S2 standard is based on the newer and more efficient H.264/MPEG-4 AVC compression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirement.

In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their mains electrical supplies.

The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.

Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. (It has been suggested that the 16:9 ratio was chosen as being the geometric mean of 4:3, Academy Ratio, and 2.35:1, the widest cinema format in common use, in order to minimize wasted screen space when displaying content with a variety of aspect ratios.)

An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC's R & D establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines).

It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an "enhanced" television format rather than a true HDTV format,[5] and so was not included, although 1920x1080 and 1280x720p systems for a range of frame and field rates were defined by several U.S. SMPTE standards.)

The demise of analog HD systems

However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK's MUSE required over four times the bandwidth of a standard-definition (SDTV) broadcast, and despite efforts made to shrink the required bandwidth down to about 2 times that of SDTV, it was still only distributable by satellite. In addition, recording and reproducing a HDTV signal was a significant technical challenge in the early years of HDTV. Japan remained the only country with successful public broadcast analog HDTV, known as "Hi-vision," featuring a 5:3 aspect ratio screen with 1,125 interlaced lines (1,035 active lines) at the rate of 60 fields per second. The single satellite transponder MUSE service was turned off on January 1, 2007.

In Europe, analog 1,125-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.

Inaugural Digital HDTV Public broadcast

HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies and MIT. (The Grand Alliance includes AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson, and Zenith.)[6] On April 6, 1997, CBS went on the air with WCBS-HD from the top of the Empire State Building, New York, doing demos and evaluations.[7] Astronaut John Glenn's return to space, on board the Space Shuttle Discovery wasn't the only thing launched on October 29, 1998. The American Advanced Television Systems Committee (ATSC) HDTV system had its public launch during the live coverage of the lift-off.[8] The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.[8] The broadcast was made possible by the Harris Corporation, which sponsored the equipment necessary for transmitting and receiving the broadcast.[8] The broadcast was hosted by former CBS News anchor, Walter Cronkite, former Gemini/Apollo era astronaut Pete Conrad and former NBC News anchor Mary Alice Williams.[9]

Modern digital compression and standardization

Digital compression methods such as MPEG-2 and H.264/MPEG-4 AVC allow the bandwidth of a single analog TV channel (6 MHz in the US) to carry up to 5 standard-definition or up to 2 high-definition digital TV channels instead.

Most developed nations have plans in place for a transition to digital television, but not necessarily (or exclusively) to HDTV.

For example, as of February 17, 2009, the U.S. terminated all full-power terrestrial analog broadcasting (although some smaller local stations have later deadlines), with both standard definition TV (SDTV) and HDTV being allowed.[10]

Current HDTV broadcast standards include ATSC (North America, parts of Central America and South Korea), DVB (Europe, Australia, parts of Asia, South America and Africa), and ISDB-T (Japan, Brazil).

However, there could be future HDTV interoperability issues.

The Chinese HDTV system uses an Intellectual Property free MPEG-2 CODEC that may have some coding interoperability issues with current DVB CODECs

The Brazilian HDTV system uses H.264/MPEG-4 AVC (as opposed to MPEG-2, the DVB standard) for the video coding, a potential source of interoperability problems

The fundamental DVB resolution (720, 1080) and frame rate specifications (24, 25, 30/29.97) have not been modified by any modified DVB HDTV system in current use or development

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. An HDTV compatible television set will not improve the quality of SDTV channels. It will make it even worse because of scaling artifacts. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

Over the air with an antenna. Most cities in the U.S. with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer high definition televisions have an HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.

Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.

Satellite-based TV companies, such as Digit-Alb (in Albania), Astra (in the Netherlands), Premiere (in Germany), DirecTV and Dish Network (both in North America), Sky Digital, and freesat (in the UK and Ireland), Bell TV and Star Choice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.

Video game systems, such as the PlayStation 3 and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output an HD signal. The Xbox Live Marketplace, iTunes Music Store, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but generally at lower bitrates than a Blu-ray Disc.

Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to an HDTV.

A DVD-R disc (~4.7GB-9GB) can also provide storage for up to 3 hours of HD video content, readable by a Blu-ray player, PlayStation 3 video game console or Blu-ray drives installed on PC towers, depending on encoder settings.[12]

Notation

HDTV broadcast systems are identified with three major parameters:

Frame size in pixels is defined as number of horizontal pixels x number of vertical pixels, for example 1280 x 720 or 1920 x 1080. Often number of horizontal pixels is implied from context and is omitted.

Scanning system is identified with the letter p for progressive scanning or i for interlaced scanning.

Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used. Recently the uniform notation of specifying number of frames per second both for progressive and interlaced video became increasingly popular.[13]

If all three parameters are used, they are specified in form frame size scanning system frame rate. Often, one parameter can be dropped if its value is implied from context. In this case the remaining numeric parameter is specified first, followed by the scanning system.

While 50Hz systems have only three scanning rates: 25i, 25p, and 50p, 60Hz systems operate with much wider set of frame rates: 23.98p, 24p, 29.97i/59.94i, 29.97p, 30p, 59.94p, and 60p. In the days of standard definition television, the fractional rates were often rounded up to whole numbers, like 23.98p was often called 24p, or 59.94i was often called 60i. High definition television allows using both fractional and whole rates, therefore strict usage of notation is required. Nevertheless, 29.97i/59.94i is almost universally called 60i, likewise 23.98p is called 24p.

For commercial naming of a product, the frame rate is often dropped and is implied from context, for example, a "1080i television set." A frame rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second, and 50i means 25 interlaced frames per second. Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.

Standard display resolutions

Standard Definition usually refers to 480 vertical lines of resolution or more.

Resolution (W×H)

Active Frame (W×H)

Canonical Name(s)

Pixels (Advertised Megapixels)

Display Aspect Ratio (X:Y)

Pixel Aspect Ratio - Standard "4:3" (X:Y)

Pixel Aspect Ratio - Widescreen "16:9" (X:Y)

Description

ITU-R BT.601

MPEG-4

ITU-R BT.601

MPEG-4

720×480

710.85×486

480i/p

345,600 (0.3)

3:2

4320:4739

10:11

5760:4739

40:33

Used for 525-line/ (60 * 1000/1001) Hz video, e.g. NTSC-M

720×576

702×576

576i/p

414,720 (0.4)

5:4

128:117

12:11

512:351

16:11

Used for 625-line/50 Hz video, e.g. PAL-I

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Most HDTV sets contain video scalers and will "upscale" or "upconvert" the transmitted signal to that of the set's native format.

Sometimes the progressive versions of these video formats are referred to as EDTV, or "Enhanced Definition Television." This is slightly misleading, for although a progressive frame contains double the image information as that of an interlaced frame, Standard Definition is already capable of displaying progressive frames, for example in MPEG video with the appropriate "Progressive" flag set. Despite this, 480p/576p signals are not typically broadcast, an example of such would be Australia's SBS HD channel, broadcast in 576p.

High-Definition display resolutions

High Definition usually refers to 720 horizontal lines of video format resolution or more.

Video Format Supported

Native Resolution (W×H)

Pixels (Advertised Megapixels)

Aspect Ratio (X:Y)

Description

Image

Pixel

720p
1280×720

1024×768
XGA

786,432 (0.8)

16:9

4:3

Typically a PC resolution XGA; also exists as a standardized "HD-Ready" TV on the Plasma display with non-square pixels.

1280×720

921,600 (0.9)

16:9

1:1

Typically one of the PC resolutions on WXGA, also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543, Digital television, DLP and LCOS projection HDTV displays.

1366×768
WXGA

1,049,088 (1.0)

683:384
(Approx 16:9)

1:1
Approx

Typically a TV resolution WXGA; also exists as a standardized HDTV displays as (HD Ready 720p,1080i), TV that used on LCD HDTV displays.

A common native resolution used in HD Ready LCD TV panels is 1366 x 768[14] pixels instead of the ATSC Standard 1280 x 720 pixels. This is due to maximization of manufacturing yield and resolution of VGA, VRAM that comes with a 768 pixel format. Hence, LCD manufacturers adopt the 16:9 ratio compatible for the HD Ready 1080p video standard. Nevertheless, every HDTV has an overscan processing chipset to fix resolution scaling and color rendering, eg LG XD Engine, SONY BRAVIA Engine. Only when viewing 1080i/1080p HD contents under HD Ready 1080p where there is true pixel-for-pixel reproduction, and for HD ready LCD TV, do some signals undergo a scaling process which results in a 3-5 percent loss of picture.

Video Format Supported

Screen Resolution (W×H)

Pixels (Advertised Megapixels)

Aspect Ratio (X:Y)

Description

Image

Pixel

720p
1280×720

1248×702
Clean Aperture

876,096 (0.9)

16:9

1:1

Used for 750-line video with raster artifact/overscan compensation, as defined in SMPTE 296M.

1080p
1920×1080

1888×1062
Clean Aperture

2,001,280 (2.0)

16:9

1:1

Used for 1125-line video with raster artifact/overscan compensation, as defined in SMPTE 274M.

1080i
1920×1080

1440×1080
HDCAM/HDV

1,555,200 (1.6)

4:3

4:3:1

Used for anamorphic 1125-line video in the HDCAM and HDV formats introduced by Sony and defined (also as a luminance subsampling matrix) in SMPTE D11.

It should be noted that the numbers used for "HD-Ready" image resolutions do not constitute acceptable 750- or 1125-line video signals in most standards-compliant hardware; in this respect terms such as "720p" and "1080p" are mostly used for advertising, though that does not necessarily mean that HD-Ready TVs labeled in this manner are incapable of accepting those formats as input.

Additionally, the "Clean Aperture" numbers are almost always contained within the frames of their respective "Production Aperture" numbers (for example, a 1888×1062 rectangle would be contained within a 1920×1080 frame). This is to maintain compatibility with analog signals, which can often become distorted close to the edge of the frame. It also increases the chance that a digital signal being played on overscan-enabled equipment will display the entire picture visibly.

Standard frame or field rates

23.976p (allow easy conversion to NTSC)

24p (cinematic film)

25p (PAL, SECAM DTV progressive material)

30p (29.97p in drop frame) (NTSC DTV progressive material)

50i (PAL & SECAM)

50p (PAL, SECAM DTV progressive material)

60i (59.94i in drop frame) (NTSC, PAL-M)

60p (59.94p in drop frame) (NTSC DTV progressive material)

Broadcast station format considerations

Close-up view

HDTV resolution

SDTV resolution

At the least, HDTV has twice the linear resolution of standard-definition television (SDTV), thus showing greater detail than either analog television or regular DVD. The technical standards for broadcasting HDTV also handle the 16:9 aspect ratio images without using letterboxing or anamorphic stretching, thus increasing the effective image resolution.

The optimum format for a broadcast depends upon the type of videographic recording medium used and the image's characteristics. The field and frame rate should match the source and the resolution. A very high resolution source may require more bandwidth than available in order to be transmitted without loss of fidelity. The lossy compression that is used in all digital HDTV storage and transmission systems will distort the received picture, when compared to the uncompressed source.

Types of media

Standard 35 mm photographic film used for cinema projection has higher resolution than HDTV systems, and is exposed and projected at a rate of 24 frames per second. To be shown on television in PAL-system countries, cinema film is scanned at the TV rate of 25 frames per second, causing an acceleration of 4.1 percent, which is generally considered acceptable. In NTSC-system countries, the TV scan rate of 30 frames per second would cause a perceptible acceleration if the same were attempted, and the necessary correction is performed by a technique called 3:2 pull-down: over each successive pair of film frames, one is held for three video fields (1/20 of a second) and the next is held for two video fields (1/30 of a second), giving a total time for the two frames of 1/12 of a second and thus achieving the correct average film frame rate.

Non-cinematic HDTV video recordings intended for broadcast are typically recorded either in 720p or 1080i format as determined by the broadcaster. 720p is commonly used for Internet distribution of high-definition video, because all computer monitors operate in progressive-scan mode. 720p also imposes less strenuous storage and decoding requirements compared to both 1080i and 1080p. 1080p is usually used for Blu-ray Disc.

Technical details

One of the first DVB-S2 tuner cards.

Networked dual-tuner for ATSC and QAM

HDTV signals and colorimetry are defined by Rec. 709. MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts. Although MPEG-2 supports up to 4:2:2 YCbCr chroma subsampling and 10-bit quantization, HD broadcasts use 4:2:0 and 8-bit quantization to save bandwidth. Some broadcasters also plan to use H.264/MPEG-4 AVC, such as the BBC which is trialing such a system via satellite broadcast, which will save considerable bandwidth compared to MPEG-2 systems. Some German broadcasters already use H.264/MPEG-4 AVC together with DVB-S2 (Pro 7, Sat.1, and Premiere). Although MPEG-2 is more widely used at present, it seems likely that in the future all European HDTV may be H.264/MPEG-4 AVC, and Norway, which is currently in the progress of implementing digital television broadcasts, is using H.264/MPEG-4 AVC for present SD Digital as well as for future HDTV on terrestrial broadcasts. In parts of Sweden the standard is already in use for HDTV terrestrial broadcasting, reaching about 25-30 percent of the population. Brazil was the first country in the American continent to begin broadcasting H.264 AVC video and HE-AAC audio as the main program (or multi) compression and the same H.264 AVC in LDTV 240p using AAC-LC as audio for mobile DTV devices, not only mobile phones.

HDTV is capable of "theater-quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound. The pixel aspect ratio of native HD signals is a "square" 1.0, in which each pixel's height equals its width. New HD compression and recording formats such as HDV use rectangular pixels to save bandwidth and to open HDTV acquisition for the consumer market. For more technical details see the articles on HDV, ATSC, DVB, and ISDB but the ISDB-Tb used primarily in Brazil uses HE-AAC that is more flexible than AC-3 and lower royalty fees.

Television studios as well as production and distribution facilities, use the HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm serial digital interface) to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8 MHz standard-definition television channels for over-the-air broadcast and consumer distribution media, hence the widespread use of compression in consumer applications. SMPTE 292M interconnects are generally unavailable in consumer equipment, partially due to the expense involved in supporting this format, and partially because consumer electronics manufacturers are required (typically by licensing agreements) to provide encrypted digital outputs on consumer video equipment, for fear that this would aggravate the issue of video piracy.

Advantages of HDTV expressed in non-technical terms

High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.

The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen's glossary.)

Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal. Brazil opted to upgrade the ISDB-T Japanese standard to H.264/MPEG-4 AVC in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of H.264 and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.

Disadvantages of HDTV expressed in non-technical terms

In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth, reducing video quality.[15] The operators may use a format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.[16] Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance, which may be difficult because of customer confusion regarding connections.

Appropriate cabling must be used. Either HDMI or component video cables must be used to support a high-definition signal. For instance, if composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI cables provide the best picture and sound but are also generally more expensive than component cables. Component video cables are RCA cables that are color coded for proper signal. They consist of three video cables (green, blue, and red), two audio cables (red and white), and they carry an analog signal. HDMI cables carry all the video and audio in one cable using a digital signal.

As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply. For example, digital video responds differently to analog video when subject to interference. Unlike in analog television broadcasting, in which interference causes only gradual image and sound degradation, interference in a digital television broadcast will freeze, skip, or display "garbage" information. This problem is particularly pronounced in the 8VSB modulation standard used for over-the-air transmission in the United States, which is highly sensitive to dynamic multipath interference that may be introduced by moving objects between the transmitting and receiving antennas. For instance, it is impossible to receive a 8VSB-modulated HDTV signal in a moving vehicle, and it may be difficult to maintain reception during high winds in locations where large trees are situated in the line between broadcasting antenna and receiver.

In order to view HDTV broadcasts, viewers may have to upgrade their TVs at some expense. Adding a new aspect ratio makes for consumer confusion if a display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition programs and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything the appearance of being too wide or not tall enough. Alternatively, viewers may choose to zoom the image which removes content that was on the top and bottom of the original TV show.[17]

Broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. Some satellite companies may offer local HD channels as a service at additional cost (transmission comes from satellite). This leads some broadcasters to offer on-air broadcasts of local HD signals as a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues entail economic and legal disputes more than technology.

Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD DVD vs. Blu-ray Disc high definition storage format war for a period of time created confusion for consumers. This particular format war was recently "settled" with Blu-ray emerging as the victorious standard.

Contemporary systems

Besides a HD-ready television set, other equipment is needed to view HD television. Cable-ready TV sets can display HD content without using an external box. They have a QAM tuner built-in and/or a card slot for inserting a CableCARD.[18]

Recording and compression

HDTV can be recorded to D-VHS (Digital-VHS or Data-VHS), W-VHS (analog only), to a HDTV-capable digital video recorder (for example DirecTV's high-definition Digital video recorder, Sky HD's set-top box, Dish Network's VIP 622 or VIP 722 high-definition Digital video recorder receivers, or TiVo's Series 3 or HD recorders), or a HDTV-ready HTPC. Some cable boxes are capable of receiving or recording two broadcasts at a time in HDTV format, and HDTV programming, some free, some for a fee, can be played back with the cable company's on-demand feature. The massive amount of data storage required to archive uncompressed streams make it unlikely that an uncompressed storage option will appear in the consumer market soon. Realtime MPEG-2 compression of an uncompressed digital HDTV signal is also prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). Analog tape recorders with bandwidth capable of recording analog HD signals such as W-VHS recorders are no longer produced for the consumer market and are both expensive and scarce in the secondary market.

In the United States, as part of the FCC's "plug and play" agreement, cable companies are required to provide customers who rent HD set-top boxes with a set-top box with "functional" Firewire (IEEE 1394) upon request. None of the direct broadcast satellite providers have offered this feature on any of their supported boxes, but some cable TV companies have. As of July 2004, boxes are not included in the FCC mandate. This content is protected by encryption known as 5C.[19] This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not all fair use of the content.

This table illustrates total horizontal and vertical pixel resolution via box size. It does not accurately reflect the screen or pixel shape (aspect ratio) of these formats, which is either 4:3, or 16:9.

External links

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